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David M. Schultz

surrounding locations. Thus, the proposed mechanisms in this paper must include supporting evidence that a warmer column of air overlies the surface pressure trough. In addition, the sharpness of the surface trough must also match the sharpness of the vertically integrated thermal structure aloft. 3. Mechanisms for prefrontal troughs and wind shifts Sanders and Doswell (1995 , p. 510) said, “It often appears, however, that one or more wind shifts precede the zone of temperature contrast in cold fronts

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Clark Evans, Kimberly M. Wood, Sim D. Aberson, Heather M. Archambault, Shawn M. Milrad, Lance F. Bosart, Kristen L. Corbosiero, Christopher A. Davis, João R. Dias Pinto, James Doyle, Chris Fogarty, Thomas J. Galarneau Jr., Christian M. Grams, Kyle S. Griffin, John Gyakum, Robert E. Hart, Naoko Kitabatake, Hilke S. Lentink, Ron McTaggart-Cowan, William Perrie, Julian F. D. Quinting, Carolyn A. Reynolds, Michael Riemer, Elizabeth A. Ritchie, Yujuan Sun, and Fuqing Zhang

, extratropical cyclones are driven by comparatively large temperature and moisture gradients. Within these baroclinic environments, frontal boundaries separate warm, moist air from cool, dry air, resulting in highly asymmetric energy distributions to drive wind and rainfall. In addition, wind speed increases with height due to the cold-core structure of these systems. During ET, the deep warm core associated with the TC becomes shallow and is often replaced by a cold-core, asymmetric structure (e.g., Evans

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Clifford Mass and Brigid Dotson

. During the period before the bent-back trough makes landfall, the intense bent-back temperature gradient and associated winds rotate around the low in counterclockwise fashion ( Figs. 14b,c ). There is also evidence of a warm-seclusion structure as the cold air circles the low, a feature noted by Shapiro and Keyser (1990) , Neiman and Shapiro (1993) , and Neiman et al. (1993) . To explore the differences in conditions on the coast and within the western Washington interior associated with this

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Julia H. Keller, Christian M. Grams, Michael Riemer, Heather M. Archambault, Lance Bosart, James D. Doyle, Jenni L. Evans, Thomas J. Galarneau Jr., Kyle Griffin, Patrick A. Harr, Naoko Kitabatake, Ron McTaggart-Cowan, Florian Pantillon, Julian F. Quinting, Carolyn A. Reynolds, Elizabeth A. Ritchie, Ryan D. Torn, and Fuqing Zhang

-pressure conditions along the North American west coast, with highest values occurring along the coast of California and over Alaska. The atmospheric river in the western flank of the second downstream ridge ( Fig. 1c ) makes landfall in Alaska and British Columbia, resulting in heavy precipitation ( Fig. 1d ). A cold-air outbreak occurs over continental and eastern North America. Further amplification of this pattern eventually leads to a massive omega block over the west coast of North America and associated

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Roland A. Madden and Paul R. Julian

originating in southern midlatitudes is an interesting question. Based on evidencefrom Tananarive (18.8-S, 47.5-W), Yasunari (1981)speculates that the origin of the clouds might be coldair outbreaks from Southern Hemisphere midlatitudes.Murakami (1987) noted that when there was clear eastward propagation of disturbances along the equatorthere was also a strong cold surge from the southernmidlatitude Indian Ocean at 850 hPa. While this evidence is intriguing, the role of southern midlatitudes inthe active

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Volkmar Wirth, Michael Riemer, Edmund K. M. Chang, and Olivia Martius

. Kiladis , and B. Liebmann , 2002 : Upper-air wave trains over the Pacific Ocean and wintertime cold surges in tropical-subtropical South America leading to freezes in southern and southeastern Brazil . Theor. Appl. Climatol. , 73 , 223 – 242 , . 10.1007/s00704-001-0669-x Martínez-Alvarado , O. , E. Madonna , S. Gray , and H. Joos , 2016 : A route to systematic error in forecasts of Rossby waves . Quart. J. Roy. Meteor. Soc. , 142 , 196

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